PANCREATIC JUICE AND ITS ACTION UPON FOOD. 171 



the alimentary canal, and from the alimentary canal back again to the 

 bloodvessels. 



That this circulation really takes place is shown by the following 

 facts : First, if a dog be killed some hours after feeding, there is never 

 more than a very small quantity of fluid found in the stomach, just suf- 

 ficient to smear over and penetrate the half digested pieces of meat ; and 

 secondly, in the living animal, gastric juice, drawn from the fistula five 

 or six hours after digestion has been going on, contains little or no more 

 albuminous matter in solution than that extracted fifteen to thiity 

 minutes after the introduction of food. It has evidently been freshly 

 secreted ; and, in order to obtain gastric juice saturated with alimentary 

 matter, it must be artificially digested with food in test-tubes, where 

 this constant absorption and renovation cannot take place. 



The secretion of the gastric juice is much influenced by nervous condi- 

 tions. It was noticed by Dr. Beaumont, in his experiments upon St. 

 Martin, that irritation of the temper, and other moral causes, would fre- 

 quently diminish or altogether suspend the supply of the gastric fluids. 

 Any febrile action in the system, or any unusual fatigue, was liable to 

 exert a similar effect. Every one is aware how readily any mental dis- 

 turbance, such as anxiety, anger, or vexation, will take away the appe- 

 tite and interfere with digestion. ' Any nervous impression of this kind, 

 occurring at the commencement of digestion, seems moreover to pro- 

 duce some change which has a lasting effect upon the process ; for it is 

 often noticed that when any anno3 r ance, hurry, or anxiety occurs soon 

 after the food has been taken, though it may last only for a few moments, 

 the digestive process is not only liable to be suspended for the time, 

 but to be permanently disturbed during the entire day. In order that 

 digestion, therefore, may go on properly in the stomach, food must be 

 taken only when the appetite demands it ; it should be thoroughly 

 masticated at the outset ; and, finally, both mind and body, particularly 

 during the commencement of the process, should be free from any- 

 unusual or disagreeable excitement. 



The Pancreatic Juice and its Action upon the Food. 



The pancreas, which is a lobulated gland, similar in its general struc- 

 ture to the salivary glands, lies across the upper part of the abdo- 

 men in such a manner that its larger or right-hand extremity is in 

 contact with the duodenum. It is traversed in its longitudinal direction 

 by its main excretory duct, which receives, as it passes from left to right, 

 the lateral branches coming from the glandular lobules, and finally, in 

 the human subject, opens into the cavity of the duodenum, closely 

 adjacent to the situation of the common biliary duct, at about ten centi- 

 metres below the pyloric orifice of the stomach. Its secretion thus 

 enters the intestine, and mingles with the substances undergoing diges- 

 tion, almost immediately after they have passed from the stomach into 

 the duodenum. 



The arrangement of the gland and its duct is similar to the above, in 



